The present invention relates a cleaning gas for removing a polymer of tetraethoxysilane or pentaethoxytantalum without damaging a reactor, tools, parts and piping of a silicon oxide film-forming apparatus or a tantalum oxide film-forming apparatus in which tetraethoxyethane or pentaethoxytantalum is used as a starting material.
When a silicon oxide film or a tantalum oxide film is deposited by a CVD (Chemical Vapor Deposition) using tetraethoxysilane (TEOS) or pentaethoxytantalum (PETa) as a starting material, a compound or polymer containing C, H and O in addition to Si and Ta is deposited at an inner wall, tools, parts and piping of the apparatus. Due to formation of these compounds, particles are formed in the reactor or clogging of the piping is occurred. Accordingly, it is necessary to remove these deposited materials at any time.
As a method for removing these deposits, it has generally been used a method of removing them by disassembling apparatus and piping. Also, the inventors of the present invention have disclosed a cleaning method using a HF gas in a Japanese Patent Provisional Application No. 5-214339. This method has arranged to rapidly react and remove polymers such as tetraethoxysilane without disassembling the apparatus and piping, or effecting removal of tools. More specifically, this method functions to remove the deposit without liquefying H.sub.2 O which is a reaction product at the time of cleaning, i.e., without causing formation of hydrofluoric acid by controlling a gas temperature and a HF gas concentration. However, if a deposition amount of polymer becomes extremely large, for example, when a flow rate of TEOS which is a starting material for increasing a deposition rate of a silicon oxide film is increased, it becomes difficult to precisely control a gas temperature at the inside of a reactor or in a piping. Thus, when a material containing C, H and O with high contents is adhered thereon with a large amount or when a liquid-state polymer exists thereon, corrosion of metal materials may be occurred by formation of hydrofluoric acid. Accordingly, it has been desired a gas or a method which can effect cleaning without requiring precise control of the temperature or the HF gas concentration or without causing metal corrosion by hydrofluoric acid.
Further, the inventors of the present invention have disclosed a method in which oxygen is firstly introduced into the system to oxidize a TEOS decomposed material, then cleaning is carried out by a HF gas, in a Japanese Patent Provisional Application No. 9-129586. However, in such a method, an O.sub.2 treatment and a HF treatment should be carried out with two steps so that it is not effective. Also, regarding a decomposed material of pentaethoxytantalum, a method of removing it with ClF.sub.3 or F.sub.2 has been disclosed in Japanese Patent Provisional Publication No. 9-301718. However, the method uses an active fluorinating agent so that there was a possibility of causing combustion by a large amount of ClF.sub.3, etc. due to trouble of a mass flow controller or trouble of a vacuum pump or a pressure control valve, or when ClF.sub.3, etc. is flowed in a system with a high pressure. Also, with regard to TEOS, as for a mixed gas for HF and ClF.sub.3, it is disclosed in Japanese Patent Provisional Publication No. 6-173012.